Relatively compact, durable valves for the control of fluid relief flow through the piston of a shock absorber or for use in other hydraulic systems are well known, as exemplified in U.S. Pat. Nos. 3,199,636, 3,256,961 and 3,312,312 issued to de Carbon. So-called "de Carbon valves" constitute a annular disc member predeflected typically between two seating portions of the internal structure of a piston such that relief for fluid flow in one direction occurs at the outer periphery of the disc and relief for opposite flow occurs at the inner periphery thereof. Valve arrangements of this type are designated as floating discs or floating valves since the valve plates or discs are not secured or fixed at any point to the structure. While the flow metering characteristics in one direction as opposed to the other across a singular floating disc can be selected to differ to a certain extent according to the requirements of the desired application, de Carbon and similar valve assemblies possess inherent limitations in this regard. Particularly in vehicle suspension applications having flow metering valve assemblies of the type used in connection with the piston of a shock absorber, for example, ride performance can be optimized where the relationship between force or fluid pressure and velocity or fluid flow rate across the damper (hereinafter described as the "damping curve" or "damping rate") is different in directions of extension and retraction of the suspension system. Extension of the suspension system a defined herein occurs where the movable members interconnected by the damper (such as vehicle frame and body components) are moving away from one another, and retraction of the suspension occurs where the same members are moving towards one another. PG,4
More specifically, it is generally desirable to have a higher damping rate in extension than in retraction for vehicle damper applications, and a recognized problem associated with known floating valve arrangements is to obtain a sufficiently high value for the ratio of the extension damping rate relative to the retraction damping rate in the operation of such shock absorbers. While adjustment of parameters such as the inner and outer diameters of the annular floating valve in such assemblies can, to some extent, alter the damping characteristics in each direction of fluid flow, it has been found that selection of the valve ring dimensions alone will not produce satisfactory results for achieving desired high ratios for the two directions of operation.
Various alternative solutions have been proposed for increasing to some extent the ratio between extension and retraction damping rates to provide desired ride characteristics. A common theme has been to structurally modify the assembly to reduce fluid displacement at a selected portion of the valving so as to increase the resistance to the passage of damping liquid during operation in extension. For example, one design entails the provision of a conical, obstructing valve seat surface which permits variable passage of fluid in the extension direction according to the degree of bending of the valve under pressure of the liquid. Other arrangements involve the provision of baffles or spring means to increase the resistance of fluid flow so as to raise the damping curve in extension. While many of such modifications to the valve structure indeed increase the extension-retraction ratio and thus further differentiate or "separate" the damping curves, such is typically not accomplished to a sufficient degree for many performance applications. Prior art devices are therefore substantially limited in their adaptability, affecting ride development and tuning operations. Moreover, known modifications to the relatively simple de Carbon designs suggested by the prior art result in structural complications which are not preferred for operation in constrained environments.